The present invention relates to a multi-layer golf ball having a core, a cover, and at least one intermediate layer position therebetween. More specifically, the invention relates to a golf ball which has a flight and control performance acceptable for use by professional golfers and skilled amateurs, and which also has an excellent durability to cracking under repeated impact.
In addition to having a good rebound, it is important for the enjoyment of the game that a golf ball also provide the player with a good feel on impact. To impart such a feel, the cover serving as the outermost layer is generally made soft. Art to this effect has been disclosed in numerous patent publications.
For example, one disclosure for ensuring a Shore D hardness of about 50 and resilience involves blending a thermoplastic polyester elastomer or an olefinic thermoplastic elastomer into a cover material in which an ionomer serves as the base resin.
Yet, such a cover material still leaves something to be desired in terms of resilience. Improvements have thus been disclosed in which behenic acid and calcium hydroxide are added to the cover material so as to carry out a high degree of neutralization and thereby impart a high resilience. Such art is described in, for example, U.S. Pat. No. 6,838,501 (corresponding to JP-A 2002-219195) and U.S. Pat. No. 7,091,269 (corresponding to JP-A 2005-013487).
However, in the former, a non-ionomeric material having a high melt viscosity is used in the cover material, making it difficult to achieve a thin cover by injection molding. In the latter, high-speed injection molding of the cover material causes laminar separation to occur, lowering the durability of the ball.